The number of columns 2, 6, 12, 20, 30 Find the 20th number and the 99th number

The number of columns 2, 6, 12, 20, 30 Find the 20th number and the 99th number

Let's first find out the law of this column
The first one: 2 = 1 × 2
Second: 6 = 2 × 3
The third: 12 = 3 × 4
The fourth: 20 = 4 × 5
The fifth: 30 = 5 × 6
Rule: the nth is n (n + 1)
Answer: the 20th is 20 × (20 + 1) = 420, and the 99th is 99 × (99 + 1) = 9900

Fill in 1, 2, 3, 7, 22155, ()
It's better to talk about the rules

1,2,3,7,22,155,(3411)
The following number is equal to the product of the preceding two numbers plus one

Fill in 1.2.4.7.. 16.22.29 according to the rule? What is the number?

11
1+1=2+2=4+3=7+4=11+5=16+6=22+7=29

Fill in the number according to the rule: 2 / 6 / 12 / 30 / 42
The seventh number is
What's the rule of this column number? Use the formula to express it
What number is one of 9120?

1/(7*8)=1/56
The nth number is 1 / (n * (n + 1))
9120 is the 95th number

The sum of 1 / 2, 1 / 6, 1 / 12, 1 / 30 and 1 / 42 is calculated by using the above rule

1/2+1/6+1/12+1/20+1/30+1/42
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7

Observe the following equation and find out the law. Then think of two equations of the same type
9 9 25 25
1 △ 3 = 1-3 1 △ 5 = 1-5
2 2 4 4

49 49
One △ 7 = - - 7
6 6

The laws of 1, - 2,4, - 8,16, - 32 are expressed by algebraic formula,
The law of 1, - 2,4, - 8,16, - 32 is expressed by the algebraic formula X. what is the number 2007?

(-2)^(x-1)
That is, to the X-1 power of - 2
The number 2007 is to the power of 2

Fill in the blanks with the following rules: 6, 3, 8, 5, 10, 7, 12, 9, (), ()
1×2×3×4+1=25（5²）
2×3×4×5+1=121（11²）
3×4×5×6+1=361（19²）
law:

Odd terms: 6,8,10,12, (14)
Even number terms: 3,5,7,9, (11)
So the brackets are 14,11
The following rule is that the product of 4 consecutive natural numbers plus 1 is the square number
n(n+1)(n+2)(n+3)+1
=(n^2+3n)(n^2+3n+2)+1
=(n^2+3n)^2+2(n^2+3n)+1
=(n^2+3n+1)^2

7 × 8 of 13 + 7 of 6 × 13-7 of 13 are calculated by simple method

7 × 8 of 13 + 7-7 of 13
=7/13(8+6-1)
=7/13X13
=7

How to calculate 10.55 + 0.6 + 9.87

It can't be calculated simply
10.55+0.6+9.87
=11.15+9.87
=21.02